This is FRESH AIR. I'm Dave Davies in for Terry Gross, who's in New York for her appearance on "The Tonight Show Starring Jimmy Fallon." Fifty-four years after President John F. Kennedy was assassinated, conspiracy theories abound about what happened that day in Dallas. And surprisingly, new information about the assassination and its investigation is still emerging. Hundreds of previously classified documents were made public a couple of weeks ago, and 3,000 more are to be released by October. Though as you'll soon hear, President Trump may have something to say about that.

Our guest is Philip Shenon, a veteran investigative reporter who spent years researching the assassination. His 2013 book "A Cruel And Shocking Act" showed how the FBI and CIA hid important information from the Warren Commission, which was appointed by President Johnson to investigate the crime. And he found there was some reason to believe Lee Harvey Oswald could have gotten encouragement or assistance from Cubans he met in Mexico a few weeks before the assassination.

Philip Shenon spent more than 20 years reporting for The New York Times. He's also the author of "The Commission: The Uncensored History Of The 9/11 Investigation." He recently wrote about the newly released assassination files for Politico.

Well, Philip Shenon, welcome back to FRESH AIR. Why now, 54 years after the assassination, are more documents about this now becoming available?

PHILIP SHENON: This is a story that actually goes back to Hollywood in 1991 when Oliver Stone, the filmmaker and a very prominent conspiracy theorist, released his film "JFK." And you'll recall that "JFK" - the movie, which was a hit at the time - really shaped the thinking of a new generation about the Kennedy assassination and raised a million conspiracy theories about how Kennedy had died.

And as a result of the furor created by that film, Congress reacted the following year by passing a bill that forced the release of every document in the government's files that might even be tangentially related to the Kennedy assassination. And as a result of that, millions of pages of documents were made public in the 1990s that really in many ways did reshape our thinking about the assassination.

But at that time in the 1990s, about 3,600 documents were held back entirely, most of them from the CIA and the FBI because those agencies argued they somehow endangered national security. Now, under this 1992 law, everything has to be released by the 25-year deadline. And that 25-year deadline is reached in October of this year.

DAVIES: Wow, lest anyone doubt the importance or impact of popular culture. So now, some documents were released this summer, right? That was, like - what? - 3,600. Is that right?

SHENON: That's right. There had been about 3,600 documents held back. About 400 of them were released early. They were released a couple of weeks ago. The National Archives wants to release these in batches over the course of the period between now and October if they can, if the agencies don't issue a final appeal to prevent them from being public. So we got 400 last week, but that's still about 3,100 that are still held back entirely but must be released by October.

DAVIES: Right, and there's a review board that was set up by the law that governs this. And the one person who could prevent their release is the president, right?

SHENON: The irony upon ironies that the president, President Donald Trump, who is no stranger to conspiracy theories, is the guy who has the final decision here. Under the law, only the president of the United States can block the release of some of these documents. And he has until October to do that. We - I understand with a colleague of mine who - Larry Sabato, a professor at the University of Virginia. We've learned that indeed a couple of agencies will appeal, and they will urge President Trump not to release some of these documents.

DAVIES: And do we have any idea of his thinking on this?

SHENON: We don't. He seems to be otherwise occupied these days. We have been told by the White House that indeed the review is underway, and they hope to have a smooth rollout through October.

DAVIES: You know, it's hard to talk about this without recalling that during the presidential campaign, President Trump promoted the idea that Senator Ted Cruz's father, Rafael, who was a Cuban immigrant, was associated with Oswald. Do we have any idea whether there would be information about that or whether it would affect the president's thinking?

SHENON: Well, I can tell you that a lot of people are going to be searching for that. But you know, President Trump during the course of the campaign promoted this article in The National Enquirer based on a single photograph from 1963 that suggested that Oswald was somehow in contact with Ted Cruz's father. Trump promoted this as proof or at least evidence that Ted Cruz's father was somehow in cahoots with Oswald. There seems to be no other evidence of this. But it is, again, irony upon ironies that our conspiracy theorist in chief will make the decision through October as to whether or not these documents go public.

DAVIES: And is there any index or other information that tells us what some of these documents might focus on or who we might learn about?

SHENON: We have a good idea of what's in there. The stuff that's most interesting to me are the files from the Central Intelligence Agency office in Mexico City. There is, to my mind, this whole mysterious chapter in the saga of the Kennedy assassination that involves Mexico City and a six-day trip that Lee Harvey Oswald pays to Mexico City just several weeks before the assassination, where we know he's meeting with Cuban spies and Russian spies and apparently may have talked openly about his intention to kill the president. And the files from the CIA officers in Mexico City are among the group of files that have to be released by October.

DAVIES: And in the book, you write about some information - not all of it confirmed - that he may have met with people who talked about killing Kennedy. He may have spoken about killing Kennedy. Just remind us what the book - what you found about what Oswald may have done and said in that six-day trip to Mexico City before the assassination.

SHENON: Well, again, the official story told by the Warren Commission and other government investigators was that Oswald was this delusional misfit, this lone wolf whose plot to kill Kennedy could never have been foiled. But in fact it looks like Oswald, at least in Mexico City, told people that he was thinking about killing Kennedy.

And these documents released over the last couple of weeks offer a fascinating theory and a really logical theory about what may have motivated Oswald directly to kill Kennedy. And the Warren Commission really ducked entirely the question of Oswald's motives. It said it just - they thought he hated America, and that might have been the explanation for the assassination.

But in fact, these CIA documents from a couple weeks ago show that there was a real theory offered within the CIA that Oswald had read a particular newspaper article. He was living at the time in New Orleans. He was an avid newspaper reader. He was an avid reader. He spent a lot of his free time in the public libraries in Dallas and New Orleans in the final - in 1963 - that he would have seen a remarkable interview that Fidel Castro had given to the Associated Press in early September 1963, a story republished in The Times-Picayune newspaper in New Orleans, that - in which Castro made clear that he thought he was under threat of assassination by the Kennedy administration and that the Kennedy administration might face reprisals as a result of this assassination threat - the theory being that Oswald would have read that article, would have become enraged on Castro's behalf and then set out to get vengeance for Castro - to kill Kennedy before Kennedy could kill Castro. That is not to be shorthanded as Castro ordered Kennedy's assassination - no, not at all. It's just that Oswald felt he was acting in Castro's behalf by setting out to kill Kennedy.

DAVIES: Maybe we should just review. What is the evidence that suggests Oswald spoke about wanting to kill the president or that people - you know, Cubans in Mexico City talked to him about the subject?

SHENON: It's an amazing story because the source of that information - that Oswald had openly talked about killing Kennedy - was Fidel Castro himself, that the FBI had a plant that turned out to be a senior leader of the American Communist Party who went to Havana after the assassination and talked to Castro and that Castro had openly acknowledged that he knew that Lee Harvey Oswald in Mexico City had talked about killing Kennedy.

DAVIES: And there were people who remembered seeing Oswald at the time - this woman Silvia Duran, who may or may not have had a romantic relationship with Oswald. And there was a story of him going to a party at which there were these mysterious people there also - but that there was talk at some of those encounters about killing the president, right?

SHENON: Well, there is this amazing story about what is described as the twist party, you know, Chubby Checker's "Twist" was very popular in Mexico City, too. And there were witnesses after the assassination who come forward to say that they remembered seeing Oswald at a party - a twist party, that he had been invited there by this vivacious, young Mexican woman who worked in the Cuban Consulate in Mexico City, a woman named Sylvia Duran, who had apparently given Oswald his help in preparing the visa application for Cuba and that people at this party had in the past talked openly about wanting to see President Kennedy dead.

DAVIES: Yeah, and we should say that for the book, you've tracked Sylvia Duran down in Mexico. She's still alive. And...

SHENON: She is remarkably available to some journalists that she adamantly denies she had a romantic relationship with Oswald although there is evidence to the contrary. But she acknowledges that she helped them with the visa application. She says he was not at this twist party. But there's a lot of evidence from other witnesses, including members of her own family, who will tell you differently.

DAVIES: And of course Sylvia Duran, the woman in Mexico whose memory would have been very fresh in 1964, agreed to be interviewed. And Earl Warren himself, the director of the commission, declined to take advantage of that.

SHENON: So this woman Silvia Duran, whatever her actual interactions with Oswald, she was the employee at the Cuban Consulate who met with Oswald, who helped him prepare his visa application. She apparently was a very sympathetic character towards him, that she's trying to be encouraging. And you know, she was a socialist, so she and Oswald might have had a lot to talk about in terms of their shared political views.

And Silvia Duran, after much hemming and hawing, agrees to come to Washington, agrees to be interviewed by the Warren Commission. But Chief Justice Warren refuses to allow her to come. His statement is, you know, she's a communist, and we don't talk to communists. Now, Sylvia Duran is still alive. Maybe she still has more to tell us.

DAVIES: Among the information that may be released in October, declassified and released is a file about an American woman named June Cobb. Who what she? What's her connection?

SHENON: She's fascinating, and I'm delighted that people can pay attention to her story because she's this apparently very brave American woman spy who finds herself on the staff of Fidel Castro in Cuba in the very earliest days of Castro's government in Havana. She's actually gone to work for the CIA. She's feeding information back to Langley. And she really puts her life on the line to do that. We - you know, there were other - there was another prominent American who was working in Castro's government who was executed. And she must have known that if her cover was blown, she would be executed as well.

She turns up later in this story because eventually she leaves Havana. She goes to Mexico City. And she's among the people who learns about the twist party, this party that Oswald shows up at where Cuban diplomats and Mexicans sympathetic to Castro's government have been invited. And people apparently may be talking openly about the need for Kennedy to be killed. And she tells the CIA about this twist party, and this leads to a lot of second guessing within the CIA about whether or not the agency had missed important clues to possible co-conspirators in the assassination.

DAVIES: She's no longer around.

SHENON: She died a few years ago. She was living - I went in search of her. She apparently died just recently in New York City.

DAVIES: We're speaking with veteran investigative reporter Philip Shenon. His 2013 book about the Kennedy assassination is "A Cruel And Shocking Act." We'll continue our conversation in just a moment. This is FRESH AIR.

(SOUNDBITE OF MATT ULERY'S "GAVE PROOF")

DAVIES: This is FRESH AIR. And we're speaking with investigative reporter Philip Shenon. He wrote a book about the Kennedy assassination called "A Cruel And Shocking Act" and has been reviewing recently declassified documents about the assassination. He wrote about them in Politico.

Now, you wrote in your book four years ago "A Cruel And Shocking Act" - you wrote a lot about the Warren Commission. You talked to a lot of the investigators who worked on that commission which was appointed by President Johnson to look into what happened in the assassination and concluded that Lee Harvey Oswald acted alone without coconspirators.

One of the things you write about is that the FBI and the CIA were very reluctant to share everything they knew and all of their information. How much did they hide?

SHENON: They withheld a tremendous amount of information. And I think it's quite clear that many senior officials of the CIA and the FBI really perjured themselves before the Warren Commission because they did have something to hide. They had something important to hide, which is that they had known a lot about Lee Harvey Oswald before the assassination, that both of those agencies, the CIA and the FBI, both had him under surveillance and sometimes pretty aggressive surveillance in the weeks before the assassination.

And had they simply acted on the information in their own files, Lee Harvey Oswald might well have been rounded up before the assassination, and the world would be a different place today. And they wanted to hide just how much they had known about Oswald from the commission. And as a result, the commission couldn't act on a lot of evidence that might have pointed to other people who knew what Oswald was going to do.

DAVIES: And you do write that there was this remarkable letter that the director of the FBI, J. Edgar Hoover, wrote to the Warren Commission that vanished that bears on this.

SHENON: I think in my years of reporting on my book, that was the bombshell document that I just couldn't quite believe people hadn't paid more attention to it. But in June 1964, in the middle of the Warren Commission investigation, J. Edgar Hoover, the director of the FBI, sends this amazing letter to the Warren Commission saying that the FBI has learned that Oswald was apparently bragging openly in Mexico City about his plans to kill Kennedy.

I have taken this document to the surviving staff members of the Warren Commission, and they are all convinced they never saw this thing. They never saw this letter. And of course if they had seen this letter in 1964, it would've raised a million questions as to who else knew that Oswald was talking openly about killing Kennedy and what they had done with that information. Did any of those people encourage Oswald to do this? It would have raised the question of coconspirators. But again, the Warren Commission staffers, at least most of the ones I talked with, are convinced they never saw this document.

DAVIES: Wow, and we just don't know what happened to it.

SHENON: Well, it turns up many years later at the National Archives. And it turns up in the files of the CIA. And copies of it do appear eventually in the digital records of the Warren Commission. But as somebody who spent weeks of my life at the National Archives reviewing the paper documents of the Warren Commission, I could tell you I never saw that document. And I - I'm quite convinced that most staff members of the Warren Commission never saw that document either.

DAVIES: You recently wrote about a - an internal CIA history written by an - by a CIA historian about this episode. What did it conclude about the CIA's conduct at the time?

SHENON: Well, it's a - it's remarkable to discover that the CIA itself describes what happened after the Kennedy assassination as being a cover-up, that lots of clues in Mexico City, especially, were never pursued. And if they had been pursued, it might have pointed to other people who at least knew what Oswald was going to do. And one thing I've always tried to make clear is that you cannot shorthand this as, Castro did it. I don't think there's any credible evidence that Fidel Castro, personally, was involved in ordering Kennedy's assassination.

But people around Mexico City who Oswald was dealing with may have felt very differently about, you know - at the height of the Cold War, some of those people may have wanted to see John Kennedy dead, if only to save the revolution in Cuba that Kennedy seemed to want to crush. And isn't it possible that some of those people encouraged Oswald to do what he was going to do? Isn't it possible that some of those people offered help for him to escape afterwards?

DAVIES: Right, in which case, they would be accomplices, of a sort.

SHENON: Absolutely. Absolutely.

DAVIES: We've been talking about the CIA. The FBI also was not exactly cooperative with the Warren Commission. You - it actually destroyed some evidence, you write in the book. What did they have to hide?

SHENON: (Laughter) Well, again, they had plenty to hide because it turned out that the FBI had Lee Harvey Oswald under aggressive surveillance and the - in the weeks and months before the assassination - not something they wanted to admit to the Warren Commission because, of course, the question would be for the FBI, why didn't you detect the threat this man posed. And it's quite clear from the record that the FBI set out after the assassination to destroy some critical evidence about what they had known about Oswald.

There's this incredible scene just a couple of days after the assassination where the decision is made at the FBI office in Dallas to destroy a note - a handwritten note that Oswald had left for them just a few weeks earlier - in which he protested the way the FBI was surveilling him, the degree of surveillance. He may have apparently threatened some sort of violent act, at least according to some FBI officials. But that document was shredded and flushed down the toilet.

DAVIES: Wow. Clarence Kelley, who was the FBI director after J. Edgar Hoover, reviewed all this material when he came in - reviewed this material about the surveillance and Oswald's visit to Mexico. What did he conclude?

SHENON: Well, Clarence Kelley is a - I think it's a remarkable testament to how much of the official story about the assassination's really never been told. But Clarence Kelley considers himself sort of an armchair detective on the question of the Kennedy assassination. And after he replaced J. Edgar Hoover at the FBI, he'd made it a task to go back and read through the raw material about the assassination and about Oswald.

And his conclusion was that, in fact, there had been a cover-up within the FBI, that this handwritten note that Oswald had left for the FBI had indeed been destroyed - he would confess that publicly later - and that the story about Mexico City - the story about the encounters with Cuban spies, and Soviet spies and others who might've encouraged Oswald to kill Kennedy - that nobody'd ever gotten to the bottom of it.

And Clarence Kelley's big conclusion, at the end of his life, was that the Kennedy assassination could have been prevented - and easily prevented - if the FBI and CIA had just acted on the information in its own files in November 1963.

DAVIES: Philip Shenon is an investigative reporter. His 2013 book about the Kennedy assassination is "A Cruel And Shocking Act." We'll hear more from Shenon after a break. And we'll meet actress Aubrey Plaza from "Parks and Recreation." She plays a woman obsessed with an Instagram star in the new film "Ingrid Goes West." I'm Dave Davies, and this is FRESH AIR.

DAVIES: This is FRESH AIR. I'm Dave Davies in for Terry Gross, who's in New York for her appearance on "The Tonight Show." We're speaking with investigative reporter Philip Shenon. His 2013 book about the Kennedy assassination, "A Cruel And Shocking Act," deals in part with how the FBI and CIA hid information from the Warren Commission, which investigated the crime. Shenon recently wrote about newly declassified files on the assassination in Politico.

In looking at things that the Warren Commission didn't know, the name Robert Kennedy comes up, of course. He was the president's brother and was the attorney general who had, you know, prosecuted the mafia. And he publicly said he accepted the Warren Commission's conclusion that Lee Harvey Oswald acted alone - privately told people that he thought there was some kind of conspiracy. I'm wondering what we know about his interaction with the Warren Commission and whether there's new information in any of these documents.

SHENON: I've always been very troubled by Robert Kennedy's actions in the months after his brother's death, in the sense that it's quite clear that he knew much more than he was ever going to tell the Warren Commission. He is the highest-ranking government official who never submitted to questioning by the Warren Commission. He, apparently, was eager not to be questioned by them.

We know from his friends and associates that he went to his death believing that there had been, or there might well have been, some sort of conspiracy in his brother's death. And he worried that it might have been - that his brother's assassination might have been somehow blowback for the anti-Castro plots that Bobby Kennedy himself had known all about during the course of the Kennedy administration.

DAVIES: Right, so he never actually gave a sworn statement at all, and the Commission didn't insist upon it.

SHENON: They only insisted - well, he sent word to the Warren Commission that he did not want to be interviewed. He instead submitted a very brief letter in which he said he had no evidence of a conspiracy. But if you go back and read that letter, you can see it's evasive, if not untruthful, about what Bobby Kennedy really knew and what he really suspected.

DAVIES: So as you've looked at more, and more and more material about the assassination, are you pretty certain that Lee Harvey Oswald was the only gunman in Dallas that day?

SHENON: I think all the most credible, scientific evidence available to us shows that Oswald was the gunman in Dealey Plaza. We'll never be able, totally, to rule out the idea that there was a second gunman because this scientific analysis is really much more art than science. But all of the most credible, technical, scientific research suggests that Oswald was the gunman in Dealey Plaza.

DAVIES: Right, and the widely ridiculed single-bullet theory, that one bullet went through Kennedy's throat - right? - and then through John Connally's body, and into his leg and wrist - best explanation?

SHENON: The best explanation - and a lot of scientific research has gone on in the years since the assassination - a lot of scientific technique that was not available in the 1960s that supports the single-bullet theory, even though it is easily the most controversial finding of the Warren Commission and easily the one I hear the most about every time I suggest that it might be true.

DAVIES: What do we know about Jack Ruby, the guy who killed Oswald the Sunday after the Friday assassination?

SHENON: Ruby was a very troubled man. You know, people in Dallas knew him well before the assassination. He was really considered sort of a misfit, a loser. And Ruby explained later that he killed Oswald because he wanted to spare Jacqueline Kennedy the need to return to Dallas to testify in a trial if Oswald was put on trial.

And people who knew Jack Ruby said that made sense, that he loved President Kennedy. He was shattered by the assassination. And he, indeed, did want to protect Jacqueline Kennedy. That - there's no evidence, they felt, that Ruby was acting under anybody's instructions. And knowing what we know about Jack Ruby, that makes sense. He was a very troubled misfit, who - you can't imagine him - that right-minded people in American organized crime would choose that guy to carry out, you know, what would've been the crime of the century.

DAVIES: And yet, again, coming back to the Warren Commission, I believe there was a point at which Jack Ruby in prison said he wanted to go to Washington and tell the true - tell the real story that he wouldn't tell in a Dallas jail, right? And then the Warren Commission didn't bring him up.

SHENON: Well, that's a confusing bit of testimony from Ruby. Chief Justice Warren goes to Dallas to interview Jack Ruby. Now, we should be clear that psychiatrists for both the defense and for the government had interviewed Ruby in the weeks previous and found him to be seriously mentally ill and delusional.

And at one point during the deposition by Chief Justice Warren, Ruby makes the comment that he can't tell the story in Dallas, he can only tell it in Washington - won't the chief justice please take him to Washington so he could tell his story? - suggesting that there might be some other conspiracy that Ruby is going to expose. Chief Justice Warren turns him down. But I will tell you, if you look at the whole body of that deposition, this is Ruby saying over, and over and over again that he acted alone.

He's later interviewed a second time, this time on a polygraph machine, and makes the same claim, that there is - that he acted alone. There's no evidence of a conspiracy. And I don't think any credible evidence of a conspiracy involving Ruby has ever emerged.

DAVIES: So we may have another 3,000-odd documents coming from the archives about the Kennedy assassination. Are you prepared to dive into them?

SHENON: (Laughter) I'm a little concerned, actually. It's so - it's about 3,100 documents that nobody's - in the public has ever seen before. And then, on top of that, there are something like 30,000 other documents that we've seen before in part that are supposedly going to be released in full. And I should tell you that these documents that were released a couple of weeks ago - I don't think anybody's been through all of them yet.

And many of them are very confusing. Some of them are illegible. You can't make out what is on them. Others are in foreign languages. Others are filled with, you know, CIA code names, and pseudonyms and the - and identify secret informants we've not been acquainted with before. I think people are going to be poring over these documents to make sense of them. Just these - the small handful from a couple of weeks ago, that - we're not going to know, really, what's in there for months, if not years. And again, they represent only a fraction of what is still hidden at the National Archives.

DAVIES: And how does the release occur? Are they posted online?

SHENON: The National Archives put them on its website early one morning a couple weeks ago without any advance notice. And it turned out that their servers were overwhelmed, and it became impossible to download those documents for the first day or two. And again, we have many, many, many more documents that are supposed to be released by October. I think the logistics of this are kind of nightmarish.

DAVIES: Yeah, I'm sure there are plenty of citizens that would love to just spend their late hours looking at this stuff. I suspect that there's a community of serious Kennedy assassination researchers, and you probably know each other. Do you communicate about this stuff?

SHENON: Sure. And there is indeed this army of researchers and just private citizens who have become knowledgeable if not obsessed with this subject for years and years, and they're poring over the documents. I will say that they all fall into camps. There are people who fall into the Mafia camp. There are people in the Castro camp. There are people who fall into, you know, rogue CIA agent camp. And I think if there's really a bombshell hidden in these documents, that army of investigators and researchers will find it eventually.

DAVIES: And so you wait for them to pop it up on social media or - they don't give you a call and say, oh, my god, Philip, did you see this?

SHENON: Well, unfortunately I have sort of a difficult relationship with so many of them because I've not embraced their conspiracy theories. But I - you know, whatever information they find, I welcome it. And I try to be as open-minded as I can about what they're finding and what the implications of it may be.

DAVIES: Do you think you'll be doing this the rest of your life?

SHENON: You know, I desperately don't want to fall down the rabbit hole of the Kennedy assassination. You know, people do become obsessed with this. It is fascinating. I think it's - you know, it is the event in my lifetime that changed the way Americans think about their government and about truth.

And it's really made so much of our - you know, I think you can look back to the Kennedy assassination as the event that turned so much of our public conversation toxic and full of conspiracy theories and full of the assumption that we're not being told the truth by our government. And trying to bring as much truth as possible to what can be determined about this, I think there's real value to that today.

DAVIES: Well, Philip Shenon, thanks for speaking with us again.

SHENON: Thank you.

DAVIES: Philip Shenon recently wrote about newly declassified documents in Politico. His 2013 book about the Kennedy assassination is "A Cruel And Shocking Act." Coming up, actress Aubrey Plaza talks about "Parks And Recreation" and her new film "Ingrid Goes West." This is FRESH AIR.